You don't have to name THREE, of course, if only one or two occur to you, but I just like the number three as it's not only a prime number but also a part of the Fibonacci sequence (on the basis of which, evidently, all life is organized - which is a spellbinding fact that if it doesn't serve to prove there's a god of some kind, then it surely must serve to prove that there isn't one of any kind. Or something.) 5 is, thus, another good number, or 13; and 4 and 7 are ok, but, well, less good, for sure. :D
So, why should you do English lessons with a trained, experienced, capable, prepared professional? Why not just "wing it" with someone whose pedagogical knowledge and linguistic aims are as weak, despite meaning well, and who'll expect YOU to do plenty of "teaching", to boot, albeit "free of charge"?